WASHINGTON -- The nation's top health official challenged insurers on Wednesday to join President Barack Obama's push to overhaul the medical system, arguing that if the effort fails it will hurt them as well as other Americans.

Obama was expected to speak Wednesday in suburban St. Louis and then travel to northeastern Ohio on Monday, his third health care event in a week. His speech comes as congressional Democrats stand on the brink of delivering the president a dramatic success with passage of his massive overhaul legislation -- or a colossal failure if they can't get it done.

As part of the administration's campaign, Health and Human Services Secretary Kathleen Sebelius sketched out a stark choice for insurers: oppose reform and eventually lose customers, or work with the White House to improve the legislation.

She told insurers in a speech that if the overhaul fails, premiums will continue to rise and employers will cancel coverage. She said the industry may make money initially, but ''this kind of short-term thinking won't work in the long run for the American people or our health care system. It won't work for you.''

Sebelius called on insurers to take the millions they might spend on attack ads and give Americans relief from rising double-digit premium increases.

Groups that oppose the legislation are stepping up their criticism, with the U.S. Chamber of Commerce announcing a coordinated campaign to spend as much as $10 million on ads, starting Wednesday, saying, ''Stop this health care bill we can't afford.''

Karen Ignagni, the insurance industry's top lobbyist, said the companies don't believe the legislation will reduce costs. The industry is preparing a list of cost control ideas for Obama.

But Sebelius' speech calmed the war of words between the administration and insurers -- at least temporarily.

''I am certainly not here to vilify the hard-working employees of insurance companies ... or blame insurance companies for all the problems in our system,'' she said.

Ignagni, who has accused the White House of waging a ''campaign of vilification,'' told reporters afterward she appreciated the gesture. ''We think now could be the beginning of a change, and we could move from vilification to problem-solving,'' she said.

Leaders in the House and Senate are awaiting a final cost analysis from the Congressional Budget Office in the next day or so that will allow them to start counting votes -- and twisting arms -- in earnest. In the House, in particular, getting the needed majority will be touch and go.

The two-step congressional approach now being pursued calls for the House to approve a Senate-passed bill from last year, despite House Democrats' opposition to several of its provisions. Both chambers then would follow by approving a companion measure to make changes in that first bill.

Republicans are playing on House Democrats' suspicions of their Senate colleagues, arguing that Senate Democrats may not hold up their end of the bargain and the votes will be damaging politically for Democrats in November.